The invention concerns actuation systems which rotate stator vanes in gas turbine engines.
The compressor in the modern axial-flow gas turbine engine is commonly equipped with variable stator vanes. FIGS. 1 and 2 illustrate the function of the stator vanes. They are views from outside a compressor having transparent walls, looking toward the axis of rotation, and looking at the tips of the blades.
These Figures are not drawn to scale, and are not aerodynamically accurate in detail. They are presented solely to illustrate the principle of using stator vanes to change the angle-of-attack of incoming airstreams to a compressor stage located downstream of the stator vanes.
FIG. 1 illustrates two stages 3 and 6 of a compressor. Incoming air, travelling in the direction of vector 9, is compressed by the first stage 3. Vector 9 is drawn as horizontal on the page. However, the direction of air actually seen by the first stage 3 is the vector sum of (1) vector 9 and (2) the velocity of the stage 3. Vector 12 represents the velocity, and vector 15 represents the vector sum.
Vector 15 represents a particular angle-of-attack at which the first stage 3 encounters the incoming air 9. After the first stage 3 compresses the air it discharges it in a different direction, represented by vector 18. Not only will vector 18 lie in a different direction than vector 9, but its velocity will be greater, because of the compression process. Vector 18 does not necessarily represent an optimal angle-of-attack for the second stage 6.
Variable stator vanes provide a solution. If variable stator guide vanes 24 are provided, as in FIG. 2, vector 18 of FIG. 1 can be changed to vector 18A of FIG. 2, having the correct angle-of-attack. The Inventor points out that the stator vanes 24 do not rotate along with stages 3 and 6. They are stationary, although individual vanes may pivot, as will now be explained.
Many types of stator vanes are adjustable, in order to adjust the angle-of-attack seen by the compressor stage to which the stator vanes deliver discharge air. For example, they may pivot about axis 26, as indicated by arrows 27.
FIG. 3 illustrates one mechanism for adjusting the stator vanes, and FIG. 4 illustrates many of the components of FIG. 3 in simplified, schematic form. Axes 26 in FIGS. 3 and 4, namely, the axes about which stator vanes 24 pivot, correspond to axis 26 in FIG. 2. A lever 36 is connected to each stator vane. All levers for a given stage of stator vanes are connected to a movable ring, such as rings 39 and 42 in FIG. 3. FIG. 4 shows ring 39.
Each ring is rotated about axis 45, to thereby rotate its stage of stator vanes. A bell crank, such as bell crank 48, rotates each ring. For example, when bell crank 48 rotates about axis 49 in FIG. 4, link 51 causes ring 39 to rotate about axis 45. Crank 36 thus rotates about axis 26, thereby rotating the stator vane 24.
All bell cranks are constrained to move in unison, by connection to arm 54. An actuator 60, described below, moves the bell cranks in unison, through a linkage represented by arrow 63 in FIG. 5.
The Inventor has identified an improvement to this type of construction.
In one form of the invention, a mechanical actuator which adjusts positions of adjustable stator vanes in a gas turbine engine occupies a sector of reduced size on the circumference of the engine, compared with the prior art.